The present invention relates to a capacity control mechanism for a scroll compressor to be employed in automobile air-conditioning apparatus.
As a capacity-controlled type scroll compressor having a valve mechanism for opening and closing a bypass hole, there has been a configuration as disclosed in Japanese Laid-Open Patent Application No. Hei 4-179886, for example, in which a bypass hole is defined on an end plate of a fixed scroll, and a capacity control block incorporating a bypass passage enabling the bypass hole to communicate with a suction chamber formed inside the housing and a valve mechanism for opening and closing the bypass passage is constituted as a unit separate from the fixed scroll.
As another example, there is a system as disclosed in Japanese Laid-Open Patent Application No. Hei 5-280476, in which a cylinder is provided in a fixed scroll member, into which a plunger which is capable of sequentially closing a group of bypass holes communicating between the cylinder and the compression chamber is inserted.
However, in the above described prior art structure, as a gap is formed between the plunger (shuttle valve) and the cylinder wall, a bypass gas from a bypass hole communicating with a fluid pocket on the upstream side flows back from the gap to a fluid pocket on the downstream side through a bypass hole on the downstream side, it suffered a problem of an increase in the driving force and a decrease in the refrigerating capacity.
In addition, during a high-speed high-load operation, as the interior of the cylinder is in a state of high temperature and high pressure by the influence of the bypass gas, it also suffered a problem of deformation of the shuttle valve, which impedes smooth motion of opening and closing.
The present invention addresses the above described prior art problems and aims at providing a high-reliability capacity-controlled scroll compressor in which the discharge capacity can be smoothly changed with a simple and compact structure.
In achieving this purpose the present invention employs as the shuttle valve a stepped cylindrical or columnar configuration with at least two different circular cross sections. With this structure, it is possible to configure a bypass gas passage from each of the bypass holes communicating with fluid pockets as respective independent communicating passages via different stepped cylindrical or columnar portions of the shuttle valve. Also, by employing a stepped configuration for the shuttle valve, strength and rigidity of the shuttle valve itself can be enhanced and thus deformation due to pressure or heat can be prevented. Furthermore, by making the passages independent, back flow from the upstream side to the downstream side can be prevented thus increasing the compression efficiency.
In other words, the invention as described in Claim 1 is one in which the shuttle valve is of a stepped cylindrical or columnar configuration having different outer diameters so as to prevent the deformation of the shuttle valve itself by increasing the strength and rigidity. The invention as described in Claim 2 is one in which the strength and rigidity of the shuttle valve is further enhanced and the machinability improved by making the stepped portion of the shuttle valve tapered.
By employing this structure, a smooth operation of the shuttle valve is possible even inside a high-temperature, high-pressure cylinder during a high-load operation, and a capacity-controlled operation with a good response can be assured over a range from a maximum capacity operation to a minimum capacity operation.
The invention as described in Claim 3 is one in which a ring groove is provided on the outer peripheral surface of the shuttle valve so that a sealing member can be fitted.
By employing this structure, as a compression gas from a bypass hole communicating with a fluid pocket on the upstream side can be completely returned to a suction chamber without flowing back into a bypass hole communicating with a fluid pocket on the downstream side by flowing down the gap between the cylinder and the shuttle valve, pressure loss is minimized and capacity-controlled operation with a high control efficiency can be assured.
The invention as described in Claim 4 is one in which the shuttle valve is of a hollow structure so as to be formed by forging enabling to attain enhanced strength and lower cost.
Also, the invention as described in Claim 5 is one in which a spring guide is formed on an end of the shuttle valve so as to prevent buckling of the spring supporting the shuttle valve.